Children with arrhythmogenic right ventricular cardiomyopathy (ARVC) are at high risk for sudden cardiac death secondary to arrhythmia. However, indications for implantable cardioverter defibrillators (ICDs) for primary prevention in children with ARVC are unclear. We present three cases of childhood-onset ARVC and discuss the indications of ICD for primary prevention. Case 1 is a 23-year-old woman who was diagnosed with ARVC at the age of 13 years with heart failure. ICD was placed for asymptomatic nonsustained ventricular tachycardia (NSVT) in recent years. Case 2 is an 18-year-old girl who was diagnosed at the age of 14 years with exertional chest pain and biventricular heart failure, which progressively worsened. She was registered for heart transplantation, and a cardiac resynchronization therapy defibrillator was implanted because of sinus bradycardia. Case 3 is an 18-year-old boy who had bigeminal premature ventricular contractions (PVCs) during a heart disease screening in school at the age of 12 years. Although cardiac function was preserved, he had multifocal PVCs and NSVTs even at rest. Although the PVC and NSVT events did not increase after restricting exercise and β-blocker administration, ventricular fibrillation developed at the age of 15 years. Therefore, the ICD was implanted. Based on these cases, the severity of arrhythmia did not necessarily correspond with the right ventricular function in patients with ARVC. Thus, the risk of fatal arrhythmia should be continuously assessed to determine the appropriate timing of ICD placement for primary prevention.